This invention relates to a liquid-liquid extraction process for the recovery of copper values from aqueous solutions employing an extractant comprising one or more hydroxy-oximes and one or more alpha, beta-dioximes and to novel alpha, beta-dioxime compounds.
The ability of certain compounds having oxime groups (&gt;C=N--OH) to form chelate complexes with metal values is well known. This property of oxime compounds has been exploited in processes developed for the recovery, by means of liquid-liquid extraction, of various metal values from aqueous solutions, for example those solutions which result from the leaching of ores. Such processes commonly involve the contacting of a metal value containing aqueous solution with an extractant comprising a suitable oxime ligand, generally a hydroxy-oxime compound, and an organic solvent. Through the contacting of these two essentially immiscible solutions, oxime/metal value complexes are formed which are preferentially soluble in the organic phase. Thus the extraction process involves both formation of metal value complexes and transfer of these complexes from the aqueous solution into the organic solution.
Such an extraction process is generally one step in the commercial operation for metal value recovery from ore leachate. Subsequent to the extraction of metal values from the aqueous phase into the organic phase, the phases are separated and the organic solution stripped with a strongly acidic aqueous solution to break the complexes and transfer metal values into a second aqueous solution. Finally, the metal values are recovered from this second aqueous solution as salts by crystallization or as elemental metal(s) by electrolysis. In its entirety, the operation results in the recovery of metal values in concentrated form and in the separation of desirable metal values which readily form oxime complexes, e.g. copper, from those which do not, e.g. iron.
A large number of oxime compounds have been proposed for use as extractants in such metal value recovery processes. British Pat. Nos. 1,091,354; 1,322,532; 1,421,766; and 1,440,917 all disclose the use of various hydroxy-oximes in metal value extractant compositions. Several such hydroxy-oxime based extractants are at present commercially applied for metal-value extraction. Furthermore, combinations of hydroxy-oximes and other mono-oxime compounds, generally aliphatic oximes, have been investigated, as disclosed in U.S. Pat. No. 3,428,449, South African Pat. No. 7,601,803, and British Pat. No. 1,091,354, and found to be particularly effective in such extractants.
Dioxime compounds alone are known to have utility in copper-value extraction applications, as evidenced by U.S. Pat. No. 3,703,573 and by the publication "Extraction of Cu(II), Ni(II), Co(II) and Fe(II) by Aliphatic alpha-Hydroxyiminoketones and alpha-Dioximes," A. R. Burkin and J. S. Preston, J. Inorg. Nucl. Chem., Vol. 37 (1975), pp. 2187-2195.
These references subscribe to the commonly recognized theory that the hydroxy-oxime or dioxime complexes with metal values of valence two are characterized as containing two molecules of the hydroxy-oxime or the dioxime for each metal ion. For illustration, U.S. Pat. No. 3,703,573 to G. C. Blytas represents an alpha, beta-dioxime/copper complex by the structural formula: ##STR1##
Metal value extraction processes, though apparently well defined and successfully operated, are not without problems and limitations. The economics of the process for recovering copper values from dilute ore leachate solutions using the relatively expensive hydroxy-oxime extractant compounds has heretofore restricted commercial application of the process. A principal source of inefficiency in the conventional extraction process for copper value recovery lies in the relatively slow rate of formation of the oxime/copper value chelate complexes. Accordingly, the discovery of an extractant composition capable of extracting copper values at a substantially improved rate is highly desirable.